USH2A and respiratory distress syndrome in premature infants: The most frequent genes associated with IRDs in Germany are ABCA4 (19.2 % of solved or likely solved families), USH2A (5.9 %) and RPGR (5.5 %) in a recent study [12] and ABCA4 (20 %), PRPH2 (8 %) and USH2A and BEST1 (both 6 %) in the present study.